Measurement devices that provide immunological specificity and electrochemical convenience for large-scale drug testing to assess the impact of various work place drug abuse strategies are needed. We propose to evaluate and develop a new test strip design that combines the advantages of immunoassay and electrochemical response. The general objective is to develop an electrochemical immunoassay capable of detecting small (hapten-sized) antigens. The specific Phase I objective is to prove the principle of separationless, solid-phase electrochemical enzyme immunoassays to detect the major metabolites of cocaine and tetrahydrocannabinol (THC) in urine. Phase II will develop this immunoassay into a commercial reagentless test strip. The proposed device consists of two major elements: (1) a disposable test strip having an electrical conducting layer containing absorbed immuno-components, and (2) the electronic components used to read the signal from the test strip. The expected result is an enzyme immunoassay electrode for drug use diagnosis, based on the principle of coupling the immunochemical reaction to the electrode response. The three researchers submitting this proposal have collaborated successfully to develop prototype enzyme-based biosensor technology which will be a crucial component for the research and development described in this proposal. Practical electrochemical sensors for the major metabolites of cocaine and THC in human urine will have great commercial viability as simple inexpensive drug use screens of personnel engaged in public safety or other high-risk activities (e.g., operating automobiles, public transportation, and military hardware).